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Jordi Marsal and Joan Girona

Relationships between midday (Ψmd) and predawn (Ψpd) leaf water potential, stomatal conductance (gs), and net CO2 assimilation rate (A) were determined at different fruit growth stages and for 2 years with different fruit loads in a `Sudanell' peach [Prunus persica (L) Batsch] plot subjected to two regulated deficit irrigation (RDI) strategies plus a control irrigation treatment. A postharvest RDI (PRDI) treatment was irrigated at 0.35 of the control after harvest. The second treatment (SPRDI) applied RDI during Stage II, the lag phase of the fruit growth curve, at 0.5 of the control and postharvest at 0.35 of the control. The control treatment and the PRDI and SPRDI when not receiving RDI were irrigated at 100% of a modified Penman crop water use calculation (ETo) in 1994, a full crop year, and 80% in 1995, a year of nearly zero crop. In 1995, with 80% of the 1994 irrigation rate and no crop, the Ψmd was higher, probably because of the lower crop load, while Ψpd was lower, probably because less water was applied to the soil. The relationship of gs and A with Ψmd during Stage II was steeper than during postharvest. Low Ψmd was not indicative of a depression in gs and A in Stage III. Osmotic leaf water potential at turgor loss (Ψπ 0) as derived from pressure-volume curves was more negative during Stage III and postharvest (about -2.9 MPa) than in Stage II (about -2.7 MPa). The Ψmd measurements together with Ψπ 0 determinations seemed to be more useful to characterize peach tree water status than Ψpd under soil water deficits because of their better relationship to midday stomatal closure.

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Chuhe Chen, J. Scott Cameron and Ann Marie VanDerZanden

Leaf water potential (LWP). relative water content (RWC), gas exchange rates and 4th-derivative spectra were measured in water-stressed and normally Irrigated plank of Totem' strawberry (Fragaria × ananassa) grown in a growth chamber. CO2 assimilation rate (A) dropped sharply when LWP decreased from -0.5 to -1.2 MPa and almost ceased as LWP fell below -1.5 MPa. There was a significant but more gradual decline of A as RWC decreased form 90% to 55%. An exponential relationship with A was observed across a wide range of LWP and RWC (Rz= 0.64, 0.86, respectively). LWP was more closely related with transpiration and leaf and stomatal conductances than with A and water use efficiency. RWC was highly correlated with all gas exchange parameters.

Under moderate water stress, younger leaves maintain higher RWC and A than older leaves. There was no relationship between LWP and leaf age.

RWC and A were both negatively correlated with peak amplitudes of Ca 684 and Ca 697 and positively correlated with Ca 693 in their 4th-derivative spectra of chlorophyll. LWP had a negative correlation with Cb 640.

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Chuhe Chen, J. Scott Cameron and Stephen F. Klauer

Leaf water potential (LWP), relative water content (RWC), gas exchange characteristics, and specific leaf weight (SLW) were measured six hours before, during, and after water stress treatment in F. chiloensis and F. ×ananassa grown in growth chambers. The leaves of both species showed significantly lower LWP and RWC as water stress developed. F. ×ananassa had consistency lower LWP under stressed and nonstressed conditions than F. chiloensis. F. ×ananassa had higher RWC under nonstressed conditions, and its RWC decreased more rapidly under water stress than F. chiloensis. In comparison to F. ×ananassa, F. chiloensis had significantly higher CO2 assimilation rate (A), leaf conductance (LC), and SLW, but not transpiration rate (Tr), under stressed and nonstressed conditions. LC was the most sensitive gas exchange characteristic to water stress and decreased first. Later, A and stomatal conductance were reduced under more severe water stress. A very high level of Tr was detected in F. ×ananassa under the most severe water stress and did not regain after stress recovery, suggesting a permanent damage to leaf. The Tr of F. chiloensis was affected less by water stress. Severe water stress resulted in higher SLW of both species.

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Ana Centeno, Pilar Baeza and José Ramón Lissarrague

particularly appropriate for irrigation scheduling ( Hanson et al., 2000 ). Leaf water potential (Ψ l ) measured at different times of the day (predawn and during the day) is often used to determine plant water status. Leaf water potential measured at predawn

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Benyamin Lakitan, David W. Wolfe and Richard W. Zobel

Abbreviations: BBL, `Bush Blue Lake 274'; DAP, days after planting; g,, leaf conductance; LN, `Luna'; Pn, photosynthesis; ψ L , leaf water potential. 1 Current address: Fakultas Pertanian, Universitas Sriwijaya, Palembang 30139, Indonesia. 3 Dept

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Timothy Coolong, Susmitha Surendran and Richard Warner

market tomatoes ( USDA, 1991 ). Predawn and midday leaf water potential (Ψ L ) and leaf relative water content (RWC) measurements were initiated on 7 July 2009 and 14 July 2010. Measurements of leaf RWC and Ψ L were conducted during the same time period

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Craig E. Kallsen, Blake Sanden and Mary Lu Arpaia

moderating fruit size in ‘Lane Late’ navel oranges ( Goldhamer, 2007 ). The objective of our study was to measure the effects of differential levels of late-season water stress as quantified by reductions in leaf water potential from well-watered ‘Beck

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Alexandra García-Castro, Astrid Volder, Hermann Restrepo-Diaz, Terri W. Starman and Leonardo Lombardini

, chlorophyll fluorescence (Fv:Fm ratio), and predawn leaf water potential did not indicate the presence of stress in field-grown Passiflora ligularis during standard growing conditions. Water stress affects plant growth because cell growth is one of the most

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Krista Shellie and D. Michael Glenn

higher transpiration in apple under a temperate climate. An objective of this research was to determine whether foliar particle film increased leaf water potential and/or g S in field-grown wine grapes under varying levels of vine water stress. The

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Paongpetch Phimchan, Suchila Techawongstien, Saksit Chanthai and Paul W. Bosland

( Techawongstien et al., 1992 ). When severe wilting persisted overnight, the plants in the drought stress treatment were re-watered at the rate of the control plants. The mean values of leaf water potential, relative water content, plant height, stem diameter